Bamboo-like copper crystal particles having a highly preferred orientation

ABSTRACT

An electroplating copper layer includes bamboo-like copper crystal particles having a highly preferred orientation. The bamboo-like copper crystal particles have a long axis direction and a short axis direction, and the bamboo-like copper crystal particles have a length of 20 nm to 5 μm in the long axis direction and a length of 20 nm to 2 μm in the short axis direction. The bamboo-like copper crystal particles have a uniform particle size, and the electroplating copper layer has a major diffraction peak at a 2θ angle of about 44°.

The present invention is a divisional application of U.S. Ser. No.15/745,685, filed on Jan. 17, 2018, which is the national stageapplication of PCT/CN2017/103498, filed on Sep. 26, 2017, which claimspriority to Chinese Patent Application No. 201611037367.6, filed on Nov.23, 2016, all of which are incorporated by reference for all purposes asif fully set forth herein.

FIELD OF THE INVENTION

The present invention relates to the field of electroplating, and moreparticularly to copper crystal particles having a highly preferredorientation and a method of preparing the same by direct currentplating.

BACKGROUND OF THE INVENTION

Copper with highly preferred orientation has many excellent properties.Because copper crystal particles have highly preferred orientation,their properties are different in different orientations. For amicroscopic point of view, different crystal orientations lead differentatomic arrangements and densities, resulting in different thermodynamicand electromagnetic properties. In addition, from the chemicalreactivity point of view, different crystal orientations lead todifferent reaction rate. For example, etching rates in differentorientations of the crystal particles can be different. This isextremely beneficial for differential etching. There is no need toprotect the copper surface (e.g., dry film protection, tin protection)for selective etching. At the same time, “side erosion” and “pool”effects can also be avoided.

Copper with highly preferred orientation, however, cannot be easilyobtained, especially in the field of microelectronics. Currently, arelatively feasible method is electroplating, but this method requirespulse electrodeposition. The equipment requirements for pulseelectrodeposition are extremely high. The current density for pulseelectrodeposition is relatively low, usually less than 5 A/dm², whichresults in low production efficiency. In addition, pulseelectrodeposition cannot control the degree of preferred orientation toobtain copper crystal particles with preferred orientation.

There is a need for a convenient and efficient method for preparingcopper crystal particles having a highly preferred orientation.

SUMMARY OF THE INVENTION

In one embodiment, the present invention provides a method of preparingbamboo-like copper crystal particles having a highly preferredorientation. The method includes providing a substrate; conducting adirect current copper electroplating on the substrate in a copperplating solution at a plating current density of 3 to 30 A/dm²; anddepositing the copper crystal particles on the substrate. The copperplating solution includes copper plating additives and a copper platingbase solution; the copper base solution includes copper sulfate,sulfuric acid, and a trace amount of hydrochloric acid or sodiumchloride, and the copper base solution has a concentration of copperions of 40-60 g/L, a concentration of sulfate ions of 80-120 g/L, and aconcentration of chloride ions of 40-60 ppm; and the copper platingadditives include an accelerator, a suppressor, and a non-dye leveler,the accelerator has a concentration of 3 to 5 mL/L, the suppressor has aconcentration of 5 to 15 mL/L, and the non-dye leveler has aconcentration of 25 to 35 mL/L.

In another embodiment, the non-dye leveler is a quaternary ammonium salthaving formula (I):

in formula (I), X is Cl⁻, or Br⁻; R¹ is O, S or N; R², R³ and R⁴ areindependently selected from the group consisting of hydrogen,unsubstituted or substituted alkyl, unsubstituted or substitutedalkenyl, unsubstituted or substituted alkynyl, unsubstituted orsubstituted C₃₋₁₂Cycloalkyl, unsubstituted or substituted C₆₋₁₂ aryl,unsubstituted or substituted 3-12 membered heterocyclic, andunsubstituted or substituted 5-12 membered heteroaryl; or R² and R³ maycombine with an atom or atoms to which they are attached to formunsubstituted or substituted C₃₋₁₂cycloalkyl, unsubstituted orsubstituted 3- to 12-membered heterocyclic, unsubstituted or substitutedC₆₋₁₂ aryl, or unsubstituted or substituted 5- to 12-memberedheteroaryl; Y¹, Y², Y³, Y⁴, Y⁵, Y⁶, Y⁷, and Y⁸ are independentlyselected from the group consisting of hydrogen, halogen, unsubstitutedor substituted alkyl, unsubstituted or substituted alkenyl,unsubstituted or substituted alkynyl, unsubstituted or substitutedC₃₋₁₂Cycloalkyl, unsubstituted or substituted C₆₋₁₂ aryl, unsubstitutedor substituted 3-12 membered heterocyclic, and unsubstituted orsubstituted 5-12 membered heteroaryl; and L is selected from the groupconsisting of unsubstituted or substituted alkyl, unsubstituted orsubstituted C₆₋₁₂ aryl, and unsubstituted or substituted 3- to12-membered heterocyclyl.

In another embodiment, the non-dye leveler is

In another embodiment, the accelerator is an organosulfate havingformula (II):

in formula (II), X is O or S; n is 1 to 6; M is hydrogen, alkali metal,or ammonium; R₁ is an alkylene, cyclic alkylene group of 1 to 8 carbonatoms, or an aromatic hydrocarbon of 6 to 12 carbon atoms; and R₂ isMO₃SR₁.

In another embodiment, the organosulfate is sodium lauryl sulfate,disodium 3,3-dithiobispropane-sulphonate, or 3,3′-dithiobispropanesulfonic acid.

In another embodiment, the suppressor is polyethylene glycol,2-mercaptoethanol, polypropylene ether, or poly N,N′-diethylsaphranin.

In one embodiment, the present invention provides an electroplatingcopper layer. The electroplating copper layer includes bamboo-likecopper crystal particles having a highly preferred orientation. Thebamboo-like copper crystal particles have a long axis direction and ashort axis direction, and the bamboo-like copper crystal particles havea length of 20 nm to 5 μm in the long axis direction and a length of 20nm to 2 μm in the short axis direction.

In another embodiment, a first plurality of the bamboo-like coppercrystal particles have a preferred orientation, and the preferredorientation is a direction perpendicular to a copper substrate on whichthe electroplating copper layer is deposited.

In another embodiment, a second plurality of the bamboo-like coppercrystal particles have a second orientation, the second orientation andthe preferred orientation forms an angle of great than 0° and less than45°, and the second plurality of the bamboo-like copper crystalparticles constitutes 50-90% of all the bamboo-like copper crystalparticles.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 is an XRD (X-ray diffraction) pattern of the copper layer ofExample 1 of the present invention.

FIGS. 2A, 2B, and 2C show cross-sectional microstructure pictures by FIB(focused ion beam) of the copper layer of Example 1 of the presentinvention.

FIG. 3 shows a XRD (X-ray diffraction) pattern of the copper layer ofExample 2 of the present invention.

FIGS. 4A and 4B show cross-sectional microstructure pictures by FIB(focused ion beam) of the copper layer of Example 2 of the presentinvention.

FIG. 5A shows a cross-sectional microstructure (SEM, Mag. X5,000) of theelectroplating copper of Example 3 of the present invention. FIG. 5Bshows a cross-sectional microstructure (FIB) of the electroplatingcopper of Example 3 of the present invention.

FIG. 6A shows a cross-sectional microstructure (SEM, Mag. X5,000) of theelectroplating copper of Comparative Example 1 of the present invention.FIG. 6B shows a cross-sectional microstructure (FIB) of theelectroplating copper of Comparative Example 1 of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to embodiments of the presentinvention, example of which is illustrated in the accompanying drawings.

The present invention provides a method for preparing copper crystalparticles having a highly preferred orientation. The method does notrequire pulse electrodeposition, and can be used at a high currentdensity.

Specifically, this method uses a direct current electroplating process,and the current density for electroplating is 3-30 A/dm². The methoduses a copper plating solution that includes copper plating additivesand a copper plating base solution.

The copper base solution includes copper sulfate, sulfuric acid, and atrace amount of hydrochloric acid or sodium chloride. The concentrationof copper ions in the copper plating base solution is 40-60 g/L, theconcentration of sulfate ions is 80-120 g/L, and the concentration ofchloride ions is 40-60 ppm.

The copper plating additives include an accelerator, a suppressor, and anon-dye leveler. The concentration of the accelerator in the copperplating solution is 3 to 5 mL/L, the concentration of the suppressor is5 to 15 mL/L, and the concentration of the non-dye leveler is 25 to 35mL/L.

Preferably, the accelerator is an organosulfate, the suppressor ispolyethylene glycol, and the non-dye leveler is a quaternary ammoniumsalt.

Preferably, the suppressor is polyethylene glycol, 2-mercaptoethanol,polypropylene ether, or poly N,N′-diethylsaphranin.

Preferably, the quaternary ammonium salt has the following formula (I):

In formula (I), X is Cl⁻, or Br⁻; R¹ is O, S or N; R², R³ and R⁴ areindependently selected from the group consisting of hydrogen,unsubstituted or substituted alkyl, unsubstituted or substitutedalkenyl, unsubstituted or substituted alkynyl, unsubstituted orsubstituted C₃₋₁₂cycloalkyl, unsubstituted or substituted C₆₋₁₂ aryl,unsubstituted or substituted 3-12 membered heterocyclic, andunsubstituted or substituted 5-12 membered heteroaryl; or R² and R³ maycombine with an atom or atoms to which they are attached to formunsubstituted or substituted C₃₋₁₂cycloalkyl, unsubstituted orsubstituted 3- to 12-membered heterocyclic, unsubstituted or substitutedC₆₋₁₂ aryl, or unsubstituted or substituted 5- to 12-memberedheteroaryl; Y¹, Y², Y³, Y⁴, Y⁵, Y⁶, Y⁷, and Y⁸ are independentlyselected from the group consisting of hydrogen, halogen, unsubstitutedor substituted alkyl, unsubstituted or substituted alkenyl,unsubstituted or substituted alkynyl, unsubstituted or substituted C₃₋₁₂cycloalkyl, unsubstituted or substituted C₆₋₁₂ aryl, unsubstituted orsubstituted 3-12 membered heterocyclic, and unsubstituted or substituted5-12 membered heteroaryl; and L is selected from the group consisting ofunsubstituted or substituted alkyl, unsubstituted or substituted C₆₋₁₂aryl, and unsubstituted or substituted 3- to 12-membered heterocyclyl.

Preferably, R¹ in formula (I) is O.

Preferably, Y¹, Y², Y³, Y⁴, Y⁵, Y⁶, Y⁷, and Y⁸ in formula (I) arehydrogen.

Preferably, R², R³ and R⁴ in formula (I) are each independentlyC₁₋₆alkyl.

Preferably, R² in formula (I) is methyl, and R³ and R⁴ in formula (I)are isopropyl.

Preferably, R² and R³ in formula (I) are ethyl, and R⁴ in formula (I) isbenzyl.

Preferably, the organosulfate has formula (II):

In formula (II), X is O or S; n is 1 to 6; M is hydrogen, alkali metal,or ammonium; R₁ is an alkylene, cyclic alkylene group of 1 to 8 carbonatoms, or an aromatic hydrocarbon of 6 to 12 carbon atoms; and R₂ isMO₃SR₁.

Preferably, X in formula (II) is S.

Preferably, the organosulfate has formula (III):H₃C—(CH₂)₃—(OC₃H₆)_(m)/(OC₂H₄)_(n)—  (III).

In formula (III), n is between 1 and about 200 and m is between 1 andabout 200.

Preferably, the organosulfate is sodium lauryl sulfate, disodium3,3-dithiobispropane-sulphonate, or 3, 3′-dithiobispropanesulfonic acid.

The present invention also provides copper crystal particles having ahighly preferred orientation obtained by the above-mentioned method. Thecopper crystal particles are column-shaped crystal particles having along axis direction and a short axis direction. The copper crystalparticles have a length of 20 nm to 5 μm in the long axis direction anda length of 20 nm to 2 μm in the short axis direction.

The microstructure of the copper crystal particles indicates that theparticles have a highly preferred orientation. Specifically, the highlypreferred orientation is a direction that is perpendicular to thesurface of the plating substrate, i.e., a vertical direction. Not allthe copper crystal particles have the highly preferred orientation,i.e., a long axis direction that is parallel to this vertical direction.

Some particles may have other orientations, that is, the degree oforientation. The degree of orientation depends on two factors. First isan angle formed by the long axis direction of a copper crystal particleand the vertical direction. The angle is from great than 0° and lessthan 45°. When the angle is 0°, the long axis direction of a coppercrystal particle is parallel to the vertical direction. Second is thepercentage of copper crystal particles having an angle from great than0° and less than 45° in all the copper crystal particles. The percentageis 50 to 90%.

Further, the copper crystal particles can have different orientationswhen subjected to an annealing process. The temperature for theannealing process can be 60 to 300° C., and the annealing time can be 10to 300 minutes.

The present invention has the following advantages.

The present invention uses a copper sulfate-sulfuric acid system as thecopper plating base solution and a certain amount of copper platingadditives. The preparation method uses a direct current electroplatingprocess and realizes high-speeding plating using regular direct currentelectroplating equipment. The method also realizes a highly preferredorientation for the copper crystal particles in the in themicrostructure of the coating layer and that the degree of orientationcan be controlled.

Compared with conventional technology, first, the present invention usesa regular direct current electroplating process and reduces thecomplexity of obtaining copper crystal particles having a highlypreferred orientation via a convention method. Second, the presentinvention does not require complicated pulse rectification equipment inproduction, and thus significantly reduces the production cost. Third,the optimization of the electroplating process and the annealingcondition can realize the control of the preferred orientation andachieve the anisotropy of the coating layer. Last, the addition ofcopper plating additives increases the capacity for current density inthe electroplating process, realizes high speed plating, andsignificantly improves production efficiency.

The above description is merely an overview of the technical solution ofthe present invention, and the technical means of the present inventioncan be understood more clearly and can be carried out in accordance withthe contents of the specification.

Example 1

Copper plating additives were added to a copper plating base solution toobtain a copper plating solution. The copper plating base solutionincluded copper sulfate, sulfuric acid, and a trace amount ofhydrochloric acid. In the copper plating solution, the concentrations ofan accelerator, a suppressor, and non-dye leveler were 3-5 mL/L, 5-15mL/L, and 25-35 mL/L, respectively. The concentration of copper ions is40-60 g/L, the concentration of sulfate ions is 80-120 g/L, and theconcentration of chloride ions is 40-60 ppm. The copper plating solutionwas stirred for 1.5-2.5 hours to mix well.

The accelerator is sodium lauryl sulfate, disodium3,3-dithiobispropane-sulphonate, or 3, 3′-dithiobispropanesulfonic acid.

The non-dye leveler is

Substrates were electroplated at three different direct currentdensities, 5 A/dm², 10 A/dm² and 15 A/dm², for 15 min, 7.5 min, and 5min, respectively, using the copper plating solution prepared above.

Plating conditions are as follows:

a. Cu²⁺ from copper sulfate (50 g/L, Cu²⁺)

b. Sulfuric acid (100 g/L)

c. Chloride ion (50 ppm)

d. Suppressor S24 (10 mL/L), leveler L118 (30 mL/L), accelerator A28 (4mL/L)

e. Plating CD: 10 ASD

f. Target height: 10 μm

The XRD patterns of the copper coated substrates prepared at threedifferent current densities were measured by X-ray diffractometry andare shown in FIG. 1 .

The cross-sectional microstructure pictures of the copper coatedsubstrates prepared at three different direct current densities weremeasured by FIB and are shown in FIG. 2 .

The results show that the inventive electroplating copper is obtained atunder high plating speed (i.e., 10 ASD) and has bamboo-like structureand uniform particle size.

Example 2

Copper plating additives were added to a copper plating base solution toobtain a copper plating solution. The copper plating base solutionincluded copper sulfate, sulfuric acid, and a trace amount of sodiumchloride. In the copper plating solution, the concentrations of anaccelerator, a suppressor, and non-dye leveler were 3-5 mL/L, 5-15 mL/L,and 25-35 mL/L, respectively. The concentration of copper ions is 40-60g/L, the concentration of sulfate ions is 80-120 g/L, and theconcentration of chloride ions is 50 ppm. The copper plating solutionwas stirred for 1.5-2.5 hours to mix well.

Two substrates can be electroplated at 5-15 A/dm² for 5-15 min using thecopper plating solution prepared above. One copper coated substrate wasthen placed in a nitrogen-protected annealing furnace and annealed at200-300° C. for 0.5-2 h.

The XRD patterns of the copper coated substrates of the annealedsubstrate and unannealed substrate were measured by X-ray diffractometryand are shown in FIG. 3 .

The cross-sectional microstructure pictures of the annealed substrateand unannealed substrate were measured by FIB and are shown in FIG. 4 .

The results show that the inventive electroplating copper is obtained atunder high plating speed (i.e., 10 ASD) and has bamboo-like structureand uniform particle size.

Example 3

An inventive electroplating copper was obtained with the same platingconditions described in Examples 1 and 2. A cross-sectionalmicrostructure (SEM, Mag. X5,000) of the inventive electroplating copperis shown in FIG. 5A. As shown in FIG. 5A, the inventive electroplatingcopper has bamboo-like structure.

A cross-sectional microstructure (FIB) of the inventive electroplatingcopper is shown in FIG. 6A. As shown in FIG. 6A, the inventiveelectroplating copper is obtained at under high plating speed (i.e., 10ASD) has bamboo-like structure and uniform particle size.

Comparative Example 1

A conventional electroplating copper was obtained with the following BKMplating conditions:

a. Cu²⁺ from copper sulfate (50 g/L, Cu²⁺)

b. Sulfuric acid (100 g/L)

c. Chloride ion (50 ppm)

d. Additive A (Enthone Inc.) (12 mL/L), Additive B (Enthone Inc.) (6 mL/L)

e. Plating CD: 10 ASD

f. Target height: 10 μm

A cross-sectional microstructure (SEM, Mag. X5,000) of the conventionalelectroplating copper is shown in FIG. 5B. As shown in FIG. 5B, theconventional electroplating copper is non-oriented.

A cross-sectional microstructure (FIB) of the inventive electroplatingcopper is shown in FIG. 6B. As shown in FIG. 6B, the conventionalelectroplating copper is non-oriented and has a large size distribution.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. An electroplated copper layer comprising: a firstplurality of copper crystal particles having a first orientation, thefirst orientation being a direction perpendicular to a copper substrateon which the electroplated copper layer is deposited; and a secondplurality of copper crystal particles having a second orientation, thesecond orientation and the first orientation forms an angle of greaterthan 0° and less than 45°, and the second plurality of copper crystalparticles constituting 50-90% of a total of the first plurality ofcopper crystal particles and the second plurality of copper crystalparticles, wherein the first plurality of copper crystal particles havea length of 20 nm to 5 μm in the first orientation and the secondplurality of copper crystal particles have a length of 20 nm to 2 μm inthe second orientation; and where the electroplated copper layer isprepared by a method comprising: providing a substrate; conducting adirect current copper electroplating on the substrate in a copperplating solution at a plating current density of 3 to 30 A/dm²; anddepositing the copper crystal particles on the substrate to form theelectroplated copper layer, wherein the copper plating solution includescopper plating additives and a copper plating base solution; wherein thecopper base solution includes copper sulfate, sulfuric acid, and a traceamount of hydrochloric acid or sodium chloride, and the copper basesolution has a concentration of copper ions of 40-60 g/L, aconcentration of sulfate ions of 80-120 g/L, and a concentration ofchloride ions of 40-60 ppm; wherein the copper plating additives includean accelerator, a suppressor, and a non-dye leveler, the accelerator hasa concentration of 3 to 5 mL/L, the suppressor has a concentration of 5to 15 mL/L, and the non-dye leveler has a concentration of 25 to 35mL/L; and wherein the non-dye leveler is


2. The electroplated copper layer of claim 1, wherein the electroplatedcopper layer has a major diffraction peak at a 2θ angle of about 44°.